The present invention relates to a substrate with a liquid crystal polymeric thin film and a method for manufacturing the same and, more in particular, the present invention relates to a substrate with a liquid crystal polymeric thin film fixed in a highly oriented state which has a light-controlling function and is suitable for use in the field of optoelectronics, etc., as well as a method for manufacturing the same.
When liquid crystal material is utilized as a device, it is generally necessary to arrange liquid crystals in a predetermined arrangement (orientation) and such molecular orientation varies depending on external effects such as electric field, magnetic field, shearing force or interface. Application use of the liquid crystal materials to various kinds of optoelectronics has been developed by utilizing the light-controlling function derived from such change of orientation.
Liquid crystals are generally classified into those of high molecular and low molecular materials. High molecular (polymeric) liquid crystals have a feature in which by fixing the oriented state of liquid crystals, the polymeric liquid crystals in the state of fixing their functions are used and they are applied in a field different from that of low molecular liquid crystals. For example, there can be mentioned application uses to orientation film for low molecular liquid crystals (as disclosed in Japanese Patent Application Laid-Open (KOKAI) 61-42618), non-linear optical device (as disclosed in Japanese Patent Application Laid-Open (KOKAI) 62-201419), circular polarizing filter and notch filter (as disclosed in Japanese Patent Application Laid-Open (KOKAI) 60-191203), optical memory (as disclosed in Japanese Patent Application Laid-Open (KOKAI) 62-66990) and color compensation plate for liquid crystal display. For practical use, it is necessary that a molecular orientation is controlled at a high level. For example, a color compensation plate for a liquid crystal display, more specifically, a color compensation plate for a super twisted nematic (STN) liquid crystal display is disposed between a liquid crystal cell and a polarization plate of a STN-type liquid crystal display for eliminating coloration due to the birefringence effect inherent to the STN liquid crystal display. The color compensation plate for the liquid crystal display serves to re-arrange elliptically polarized light having elliptic coefficient and azimuth angle which are made different depending on wavelength after passing through the cell into linearly polarized light of uniform azimuth angle again. Such a function can be developed only when the liquid crystal high molecular materials are oriented horizontally at a high degree of regularity and high homogenity in a certain direction.
By the way, a method of controlling the oriented state of low molecular liquid crystals by using an orientation film has already been established, which constitutes a fundamental technique for twisted nematic or STN liquid crystal display. On the other hand, as a method of controlling the oriented state of high molecular (polymeric) liquid crystals, a technique of orienting with higher order parameters than those of the low molecular liquid crystals, for example, a method of applying external force such as shearing stress, or a method of applying external force such as electric field or magnetic field has been known in a certain restricted region for any of nematic, smectic or cholestic liquid crystals. However, there is a drawback in such a method, that the control for orientation over a large area is impossible or the uniaxial orientation within a plane can not be controlled even if horizontal orientation can be conducted. That is, it can not be said that a technique capable of highly controlling the orientation of high molecular (polymeric) liquid crystals and fixing the oriented state has been established, and accordingly, it has been demanded for providing a substrate with a liquid crystal high molecular (polymeric) thin film which is fixed in a highly oriented state.
As a result of the present inventors' earnest studies, it has been found that liquid crystal polymeric materials in a substrate with a liquid crystal polymeric thin film obtained by coating a solution comprising a polyamic acid or its derivative as the essential ingredient on a substrate, cyclizing the polyamic acid or its derivative by heating, thereby forming a polyimide film having a glass transition point of higher than 300.degree. C., applying a rubbing-treatment to the polyimide film, coating a thermotropic liquid crystal polymeric solution thereover, subjecting to heat-treatment at a temperature higher than the glass transition point of the liquid crystal polymer, and then cooling to a temperature lower than the glass transition point, are oriented in parallel with the substrate and oriented to a uniform direction within a plane in parallel with the substrate without division to domains. The present invention has been attained based on such a finding.